This invention relates to forming turbine components by additive manufacturing. In particular, this invention relates to forming single crystal turbine components by additive manufacturing.
Additive manufacturing is a process by which parts can be made in a layer-by-layer fashion by machines that create each layer according to an exact three dimensional (3D) computer model of the part. In powder bed additive manufacturing, a layer of powder is spread on a platform and selective areas are joined by sintering or melting by a directed energy beam. The platform is indexed down, another layer of powder is applied, and selected areas are again joined. The process is repeated for up to thousands of times until a finished 3D part is produced. In direct deposit additive manufacturing technology, small amounts of molten or semi-solid material are applied to a platform according to a 3D model of a part by extrusion, injection, or wire feed and energized by an energy beam to bond the material to form a part. Common additive manufacturing processes include selective laser sintering, direct laser melting, and electron beam melting.
Since a part is produced in a continuous process in an additive manufacturing operation, features associated with conventional manufacturing processes such as machining, forging, welding, casting, etc. can be eliminated leading to savings in cost, material, and time.
Early additive manufacturing products were used, for instance, for 3D design concepts, rapid prototyping of models, and other applications. In the past decade, interest has been growing in the direct fabrication of useful parts across industry.
In the gas turbine industry, methods to directly fabricate components with internal passageways, such as blades and vanes, using additive manufacturing are attracting much attention. An inherent feature of metal parts fabricated by additive manufacturing is that the microstructures are polycrystalline. A number of turbine components require a single crystal microstructure to withstand the high temperature, high stress operating environment in a hot gas stream.